An electroluminescent element has a configuration in which a light-emitting layer including a light-emitting material is sandwiched between an anode electrode and a cathode electrode, and is provided with a characteristics that a light-emission with high brightness is available with a low driving voltage. Therefore, the electroluminescent element is expected to be applied to an electro-optical device such as a display or an illumination.
In recent years, for a purpose of improving a performance as an illumination usage, researches have been conducted on improving a light extraction efficiency or making a light-emitting surface larger in area size. For example, in Patent Document 1, it is disclosed that the light extraction efficiency is improved with a light-emitting element in which a dielectric layer is formed between an anode electrode layer and a cathode electrode layer, a cavity (a concave portion) extends through at least one of the dielectric layer and the electrode layers and an inside surface of the cavity is covered with an electroluminescence coating material. Here, when numeral cavities are arranged inside of electrode surfaces and a size of each cavity and a gap between cavities are small enough, the light emission is visible as a surface light emission.
In an electroluminescent element, in general, a transparent electrode such as indium tin oxide (ITO) is used for one of the anode electrode and the cathode electrode in order to gain a high light-emitting efficiency, while a light-reflecting electrode such as a metal or the like is used for the other. A sheet resistance of ITO is higher compared to that of a metal. Therefore, between a portion near a terminal of the ITO electrode and a portion far from the terminal in the light-emitting surface, the voltage between the anode electrode and the cathode electrode comes to be different due to a voltage drop. Accordingly, when the light-emitting area is made large, a brightness distribution in the light-emitting surface becomes non-uniform.
To address such a problem, in Patent Documents 2 and 3, electroluminescent elements are disclosed in which a non-light-emitting portion is provided in a light-emitting surface with a method of arranging an insulating material between the electrodes or the like so that an area rate of the non-light-emitting portion is made smaller as a distance from a terminal of the electrode gets farther. Namely, by making an area of a substantial light-emitting portion larger at a region far from the terminal of the electrode, a brightness distribution in the light-emitting surface becomes uniform.